What oil filter would be the best overall product to run on my 21 WRX. Going to run amsoil oil and want to use a top rated filter. I know a lot of Subaru owners use the OEM filter. Is there any logical reason for this or benefit?
OEM Subaru filters have a bypass pressure rating of 23 psi. The reason it is so high is because the oil pumps in these engines have a very high flow rate, especially for such a small filter. Most aftermarket filter manufacturers do not bother designing Subaru-specific filters, and their recommended filters have a bypass rating of only 10-15 psi. These filters will bypass unfiltered oil on a regular basis. So, a lot of Subaru owners just stick with the OEM filters. They're well made filters, but not the most efficient ones out there.
For the WRX, the best non-OEM oil filter is probably the PurolatorOne PL14615. It's more efficient than the OEM filter (99% at 26 micron, vs maybe ~40 micron), and has the proper bypass rating. Purolator recommends the PL14459 for the WRX and BRZ for some reason, but it's got a lower bypass rating and is less efficient than the PL14615, which is what they recommend for most Subaru models now.
There are some other aftermarket filter brands that have filters with the proper bypass rating, but AFAIK none of them are particularly efficient, nor are they clearly better than OEM in any other way.
I prefer the PurolatorOne for my WRX. My second choice would be OEM. I wouldn't recommend anything else.
